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Healthy Housing and Environment Team
Mercury in Fish – Frequently Asked Questions
April 11, 2002
What is mercury?
- Mercury is a naturally occurring metal, which has several forms. The metallic mercury is a shiny, silver-white odorless liquid. This is the type of mercury used in thermometers. If heated, it is a colorless, odorless gas.
- Mercury combines with other elements, such as chlorine, sulfur, or oxygen, to form inorganic mercury compounds or "salts," -- usually white powders or crystals. Mercury also combines with carbon to make organic mercury compounds. The most common one, methylmercury, is produced by microscopic organisms in the water and soil. More mercury in the environment can increase the amounts of methylmercury that these small organisms make.
(Source ATSDR on-line ToxFAQs: Mercury at www.atsdr.cdc.gov/tfacts46.html)
What happens to mercury when it enters the environment?
- Methylmercury builds up in the tissues of fish. Larger and older fish tend to have the highest levels of mercury
- People can breathe in small amounts of mercury metallic if a spill occurs at home or at work.
(Source: ATSDR ToxFAQs)
What is the difference between "light" and "white" canned or packaged tuna?
Canned or packaged tuna was found to be lower in mercury than fresh or frozen tuna. There are two kinds of canned or packaged tuna on the market, labeled as light and white (albacore).
Light tuna:
- Also called "chunk light"Soft textureLower mercury
- Women of child-bearing age should not eat more than one meal* of light tuna fish per week, and young children should not eat more than 2-3 ounces per week.
White tuna:
- Also called "albacore tuna"Solid textureHigher mercury
- Should not be consumed by women of child-bearing age and young children
* Approximately 6-8 ounces of fish equals to one meal
What are the effects of mercury on my body? (source: ATSDR ToxFAQs)
- The nervous system is very sensitive to all forms of mercury. Methylmercury and metallic mercury vapors are more harmful than other forms, because more mercury in these forms reaches the brain. Mercury in the mother’s body passes to the fetus and may accumulate there. Very young children are more sensitive to mercury than adults. Exposures to high levels of mercury can permanently damage adult organs, including the brain, kidneys, and a developing fetus. Effects on brain function in adults may result in irritability, shyness, tremors, changes in vision or hearing, and memory problems.
How do you tell if mercury is present in fish?
- Mercury is odorless and colorless.
- There is no way to clean or remove mercury. It can’t be cut, cleaned or cooked out.
If I shop at a fish market, how do I know if the fish sold there are safe to eat?
Most fish contains safe levels of mercury, however, pregnant, nursing, women planning a pregnancy in the next year and small children should not eat:
- Swordfish
- Shark
- Bluefish
- Striped Bass
- Freshwater fish caught in RI (other than trout caught in stocked waters.)
- Tile Fish and King Mackerel (Although not regularly caught or consumed in Rhode Island, these species are included in FDA Advisory.)
What fish are safe to eat?
- Graphs that illustrate the four-tier fish advisory are available here.
Is there a way of measuring mercury in a fish? What level, if any, is safe?
- The Environmental Protection Agency, EPA has collected fish and sent them to a laboratory for analysis. This analysis is costly and takes time. (If you wanted to analyze the fish you bought, by the time you got the results back your fish would be too old to eat). RI adopted the EPA Ambient Water Quality Criteria of 0.3 parts per million (ppm). Fish found to have this amount of mercury or less in them are deemed "safe".
Is it safe to eat clam cakes and clam chowder from local seafood restaurants?
- HEALTH recommends that clams and other shellfish be thoroughly cooked before they are consumed. Clams get cooked in the process of making clam chowder and clam cakes. Mercury is typically not a problem in clams or other shellfish.
I fish in Massachusetts and Connecticut; is it safe to eat fish caught there?
- Neighboring states, as well as many other states in the country have their own specific fish advisories. Find out more by calling their state health departments or by going on their web pages:Massachusetts: call: 617-624-5757 or on the web at: www.state.ma.us/dph/beha
- Connecticut: call: 806-509-7742 or on the web at: www.state.ct.us/dph
Where can I learn more about fish caught in neighboring states?
- By calling that State’s Health Department and asking for information about their mercury in fish advisories, or by going on their web page as listed above.
Is there a medical test to show whether I’ve been exposed to mercury?
- Tests can measure mercury levels in the body. Consult your doctor or other health care provider to see if this is right for you.
How long has there been mercury in RI fish?
- The Food and Drug Administration has issued warnings about mercury in swordfish since 1986. The problems of mercury in fresh water fish were discovered more recently.
You say not to eat freshwater fish caught in RI water (other than stocked trout). What are the names of some of the freshwater fish that I should avoid?
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